Freeze is a status that can be split in 'cold' and 'frozen'.
All freeze durations are halved in nightmare difficulty and halved again in hell dificulty.
every player and monster can become cold, the only exeptions are monsters that are immune to cold
and players that have a cannot be frozen property on their gear.
when a player or monster becomes cold they will have a reduced movement speed, cast speed, attack speed and hit recovery.
Also when a monster is cold it will have a chance to shatter when it is slain, leaving no corpse.
Players cannot be frozen, they can only become cold.
most monster however can become frozen, when a monster is frozen it will turn blue and will completely 'freeze', it will not be able to move or fight. It will also always shatter when it is slain, leaving no corpse.
There are some monsters that cannot be frozen, this are all champions, bosses and monsters with an immunity to cold.
 Inflicting Freeze
All cold damage will cause it's target to become cold.
Some weapons also have the property: freeze target, any damage from these weapons will cause it target to become frozen.
there also are a number of skills that can inflict frozen including the amazons freezing arrow and the sorceress' frozen armor and glacial spike